Polymeric material, method of forming the polymeric material, and method of forming a thin film using the polymeric material

ABSTRACT

A polymeric material includes a pendant polycyclic aromatic compound precursor.

RELATED APPLICATIONS

The present Application is a Divisional Application of U.S. patentapplication Ser. No. 11/771,854 which was filed on Jun. 29, 2007 nowU.S. Pat. No. 7,932,128.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polymeric material which may bereliably used to make a thin film (e.g., an organic semiconductor thinfilm) having a uniform thickness.

2. Description of the Related Art

Soluble organic semiconductors have attracted much interest for use ininexpensive low-end electronic devices such as radio frequencyidentification (RFID) tags or displays. Among organic semiconductors,pentacene has shown real potential for having field effect mobilitywhich rivals amorphous silicon.

Solution processed pentacene thin film transistors (TFT) have beenformed using soluble pentacene precursors which after deposition on thesurface could be converted to pentacene by moderate heating (e.g., seeU.S. Pat. No. 6,963,080 to Afzali-Ardakani et al. entitled “THIN FILMTRANSISTORS USING SOLUTION PROCESSED PENTACENE PRECURSOR AS ORGANICSEMICONDUCTOR”; and U.S. Pat. No. 7,125,989 to Afzali-Ardakani et al.entitled “HETERO DIELS-ALDER ADDUCTS OF PENTACENE AS SOLUBLE PRECURSORSOF PENTACENE”).

However, since solutions of these precursors have very low viscosity andthe molecules have relatively low molecular weights, uniform (e.g.,uniform thickness) thin film coatings of these compounds are verydifficult to form and are sometimes not repeatable.

SUMMARY OF THE INVENTION

In view of the foregoing and other problems, disadvantages, anddrawbacks of the aforementioned compositions, methods and devices, it isa purpose of the exemplary aspects of the present invention to provide,inter alia, a polymeric material which may be reliably used to make athin film (e.g., an organic semiconductor thin film) having a uniformthickness.

An exemplary aspect of the present invention is directed to a polymericmaterial with a pendant polycyclic aromatic compound precursor (e.g., apendent pentacene precursor).

Another exemplary aspect of the present invention is directed to amethod of forming a polymeric material with a pendant polycyclicaromatic compound precursor (e.g., a pendent pentacene precursor) whichincludes forming a polycyclic aromatic compound precursor including atleast one polymerizable functionality, and polymerizing thepolymerizable functionality to form the polymeric material with thependant precursor.

Another exemplary aspect of the present invention is directed to amethod of forming a thin film. The method includes depositing a solutioncomprising a polymeric material with a pendant polycyclic aromaticcompound precursor (e.g., a pendent pentacene precursor) onto asubstrate, removing a solvent from the deposited solution to form a thinfilm of the polymeric material with the pendant precursor, and heatingthe substrate to form a thin film of the polycyclic aromatic compound(e.g., pentacene) in a polymer matrix.

Another exemplary aspect of the present invention is directed to anorganic semiconductor device which includes a thin film including apolycyclic aromatic compound (e.g., pentacene) in a polymer matrix.

With its unique and novel features, the exemplary aspects of the presentinvention may provide a material which may be reliably used to make athin film (e.g., an organic semiconductor thin film) having a uniformthickness.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of the embodiments ofthe invention with reference to the drawings, in which:

FIG. 1 illustrates a method 100 of forming a polymeric material with apendant polycyclic aromatic compound precursor, according to anexemplary aspect of the present invention;

FIG. 2 illustrates a method 200 of forming a thin film (e.g., an organicsemiconductor thin film), according to another exemplary aspect of thepresent invention; and

FIGS. 3A-3B illustrate an organic semiconductor device 300, according toan exemplary aspect of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION

Referring now to the drawings, FIGS. 1-3B illustrate the exemplaryaspects of the present invention.

An exemplary aspect of the present invention is directed to a polymericmaterial with a pendant polycyclic aromatic compound precursor. Thepolymeric material may include a polymer such as polystyrene, or otherpolymers such as poly(methylmethacrylate), poly(acrylate) or polyethers.The polycyclic aromatic compound may include, for example,oligothiophene, perylene, benzo[ghi]perylene, coronene and polyacene(e.g., pentacene, tetracene, hexacene).

FIG. 1 illustrates a method 100 of forming a polymeric material with apendant polycyclic aromatic compound precursor, according to anexemplary aspect of the present invention. The method 100 includesforming (110) a polycyclic aromatic compound precursor including atleast one polymerizable functionality. For example, the at least onepolymerizable functionality may include one of acrylate, methacrylate,styryl, and vinyl ether.

Further, forming (110) the precursor including at least onepolymerizable functionality may include reacting a polycyclic aromaticcompound (e.g., pentacene) with a dienophile. The dienophile mayinclude, for example, a compound that has at least one heteroatom suchas N, O or S, connected by a double bond to a second heteroatom orcarbon.

In particular, the dienophile may include at least one heteroatom bondedto an aromatic moiety, such as thioxonmalonates, azodicarboxylates,thioaldehyde, acylnitroso and N-sulfinylamides. For example, thedienophile may include N-sulfinyl-4-styrylamide orN-sulfinylmetacrylamide.

Further, the polycyclic aromatic compound may be reacted with thedienophile at low to moderate temperatures and in the presence of acatalyst such as a Lewis acid catalyst. The Lewis acid catalyst mayinclude, for example, titanium tetrachloride, silver tetrafluoroborateand methyl rhenium trioxide. Any residue from the dienophile remainingin the product of the reaction may be removed either by washing with asolvent or by vacuum drying.

The method 100 may also include polymerizing 120 the polymerizablefunctionality to form the polymeric material with the pendant precursor.The polymerizing 120 may include, for example, one of lightpolymerization, free radical polymerization and ionic polymerization.

The polymeric material with a pendent polycyclic aromatic compoundprecursor may be soluble (e.g., soluble in common organic solvents) andmay have a molecular weight in a range from 2000 to 100000.

FIG. 2 illustrates a method 200 of forming a thin film, according toanother exemplary aspect of the present invention. The method 200 mayinclude depositing (210) a solution including a polymeric material witha pendant polycyclic aromatic compound precursor (e.g., a pendantpentacene precursor) onto a substrate (e.g., glass substrate, metalsubstrate, polymer substrate, silicon substrate, etc.). The depositing(210) may be performed, for example, by pouring, spraying, spin-coating,dip-coating, screen printing, micro-contact printing, doctor blading,etc.

The solution may include the polymeric material dissolved (e.g.,substantially dissolved) in a solvent (e.g., an organic solvent). Thesolvent may include, for example, chloroform, tetrachloroethane,tetrahydrofuran (THF), toluene, ethyl acetate, methyl ethyl ketone(MEK), dimethyl formamide, dichlorobenzene, propylene glycol monomethylether acetate (PGMEA) or mixtures of any of these.

Further, the solution including the polymeric material may include aviscosity of at least 50 cps, but no greater than 100000 cps.

The method 200 may further include removing (220) the solvent from thedeposited solution to form a thin film of the polymeric material with apendant polycyclic aromatic compound precursor. For example, the solventmay be removed by using heat to drive off the solvent.

The method 200 may also include heating (230) the substrate to form athin film of the polycyclic aromatic compound (e.g., pentacene) in apolymer matrix. This may be performed, for example, by heating thesubstrate to a temperature in a range from about 100° C. to 200° C.

The method 200 may also include forming the polymeric material with apendant polycyclic aromatic compound precursor (e.g., a pendentpentacene precursor). As described above, the polymeric material with apendant polycyclic aromatic compound precursor may be formed by forminga polycyclic aromatic compound precursor including at least onepolymerizable functionality, and polymerizing the polymerizablefunctionality to form the polymeric material with a pendant polycyclicaromatic compound precursor.

An exemplary aspect of the method 200 may be represented by thefollowing scheme:

In this scheme, pentacene (I) may be reacted with a dienophile such asN-sulfinyl-4-styrylamide (II) in the presence of a Lewis acid catalystto give the monomeric pentacene precursor adduct (III). The styrylfunctionality of the monomeric adduct (III) may be polymerized in thepresence of light or free radical generators to form polystyrene withpentacene pendant (IV).

A film of this polymeric material (IV) may then be formed (e.g., coated)on a substrate and the solvent may be driven off to form a uniform thinfilm of this polymeric material. The substrate may then be heated at amoderate temperature (e.g., 100° C. to 200° C.) which may result in theformation of pentacene in a matrix of polystyrene.

FIG. 3 illustrates an organic semiconductor device 300, according to theexemplary aspects of the present invention. The device 300 may include athin film 310 which includes a polycyclic aromatic compound (e.g.,pentacene) in a polymer matrix (e.g., a polystyrene matrix). The thinfilm may have, for example, a thickness in a range from about 5 nm to200 nm, and in an exemplary aspect the thickness of the thin film may bein a range from about 10 nm to about 50 nm.

Further, the thin film may include a substantially uniform thickness.For example, a thickness of the thin film may vary by no greater thanabout 1.0 micrometer over the entire thin film.

For example, the organic semiconductor device may include a thin filmtransistor (TFT). Such a thin film transistor may be used, for example,in electronic devices such as radio frequency identification (RFID) tagsor displays. For example, the thin film transistor may include a channelregion (e.g., a p-type channel region) which includes the thin film.

That is, the TFT may use a thin film of polycyclic aromatic compound ina polymer matrix (e.g., pentacene in a polystyrene matrix), as anorganic semiconductor channel. Generally, the TFT may be formed bydepositing a solution including the polymeric material with a pendantpolycyclic aromatic compound precursor on a substrate (e.g., a highlydoped silicon substrate) covered with a thin film of thermally grownoxide as gate dielectric, and then heating the solution to drive off thesolvent. The substrate may then be heated to convert the thin film ofthe polymer material with a polycyclic aromatic compound precursor to athin film of the polycyclic aromatic compound in a polymer matrix.Source and drain electrodes may then be deposited on top of the thinfilm of polycyclic aromatic compound in a polymer matrix film to get aTFT device.

The TFT may also include a gate electrode such as a patterned metal gateelectrode formed on a substrate or a conducting material such as, aconducting polymer, which is then coated with an insulator. Theinsulator may include, for example, an oxide, nitride, a ferroelectricor an organic polymeric compound.

FIGS. 3A-3B illustrate an organic semiconductor device 300, according toan exemplary aspect of the present invention. As illustrated in FIG.3A-3B, the organic semiconductor device 300 may include a TFT having asubstrate 20 (e.g., glass, silicon, or plastic substrate), a layer ofdielectric 30 formed on the substrate 20. The substrate 20 may include,for example, glass, polyethylenenaphthalate (PEN),polyethyleneterephthalate (PET), polycarbonate, polyvinylalcohol,polyacrylate, polyimide, polynorbornene, polyethersulfone (PES), etc.The dielectric 30 may include, for example, silicon dioxide, siliconnitride, aluminum oxide, PbZr_(x)Ti_(1-x)O₃ (PZT), Bi₄Ti₃O₁₂, BaMgF₄,Ba(Zr_(1-x)Ti_(x))O₃ (BZT) and organic polymeric compounds like MYLAR™,Polyethylene Terephthalate, polycarbonate and polyimide.

The device 300 may, for example, be fabricated in at least two differentgeometries: top contact and bottom contact geometries as shown in FIGS.3A and 3B.

In the bottom contact geometry of FIG. 3A, a thin film of dielectric 330may be formed on substrate 320. Three contacts may then be formed on thesubstrate 320 (e.g., contact 331) and dielectric 330 (e.g., contacts332, 333), and the thin film including a polycyclic aromatic compound ina polymer matrix 340 (e.g., pentacene in a polystyrene matrix) may beformed on the dielectric 330 and contacts 332, 333. The contacts mayinclude, for example, a metal such as gold (Au), silver (Ag), nickel(Ni), indium tin oxide (ITO), chromium (Cr), etc. The device can berinsed with solvents to remove any unreacted starting materials orproducts.

In the top contact geometry of FIG. 3B, the dielectric layer 330 may beformed on the substrate 320, and the thin film including a polycyclicaromatic compound in a polymer matrix 340 may be formed on thedielectric layer 330. Then, contacts 332 and 333 may be formed (e.g.,through a shadow mask).

In summary, the exemplary aspects of the present invention may include apolymeric material with pendant polycyclic aromatic compound precursorwhich can be deposited from solution into a uniform thin film and whichafter removing the solvent(s), may be converted to polycyclic aromaticcompound. In this approach very uniform coating of polycyclic aromaticcompound may be obtained.

For example, the polymeric material may be formed by synthesizing apolycyclic aromatic compound precursor which includes at least onepolymerizable functionality (acrylate, methacrylate, styryl, vinylether, etc.), and then polymerizing the functionality to form apolymeric material with pendant polycyclic aromatic compound precursors.

In an exemplary aspect of forming a polymeric material of the presentinvention, pentacene (I) may be reacted with a dienophile such asN-sulfinyl-4-styrylamide (II) in the presence of a Lewis acid catalystto give the monomeric pentacene precursor adduct (III). The styrylfunctionality of the monomeric adduct (III) may be polymerized in thepresence of light or free radical generators to form polystyrene withpentacene pendant.

The polymeric material may be soluble in common organic solvents and,depending on its molecular weight, may form a viscous solution. A filmof this polymeric material may then be formed (e.g., coated) on asubstrate and the solvent may be driven off to form a uniform thin filmof this polymeric material. The substrate may then be heated at amoderate temperature (e.g., 100° C. to 200° C.) which may result in theformation of pentacene in a matrix of polystyrene.

With its unique and novel features, the exemplary aspects of the presentinvention may provide a material which may be reliably used to make athin film (e.g., an organic semiconductor thin film) having a uniformthickness.

While the invention has been described in terms of one or moreembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims. Specifically, one of ordinary skill in the art willunderstand that the drawings herein are meant to be illustrative, andthe design of the inventive assembly is not limited to that disclosedherein but may be modified within the spirit and scope of the presentinvention.

Further, Applicant's intent is to encompass the equivalents of all claimelements, and no amendment to any claim in the present applicationshould be construed as a disclaimer of any interest in or right to anequivalent of any element or feature of the amended claim.

What is claimed is:
 1. A polymeric material with a pendant polycyclicaromatic compound precursor, wherein said polymeric material isrepresented by the formula:

where R comprises said pendant polycyclic aromatic compound precursor.2. The polymeric material of claim 1, wherein said pendant polycyclicaromatic compound precursor comprises a pendant pentacene precursorwhich is represented by the formula:


3. The polymeric material of claim 1, wherein the polycyclic aromaticcompound comprises a member selected from the group consisting ofoligothiophene, perylene, benzo[ghi]perylene, coronene and polyacene. 4.The polymeric material of claim 1, wherein the polycyclic aromaticcompound comprises a member selected from the group consisting ofpentacene, tetracene and hexacene.
 5. The polymeric material of claim 1,wherein the polymeric material with a pendent polycyclic aromaticcompound precursor is soluble in an organic solvent and has a molecularweight in a range from 2000 to 100000.